The transforming growth factor-? (TGF?) signaling pathway appears to play dual roles in pancreatic ductal adenocarcinoma (PDAC) pathogenesis; restraining the early stages of tumor development while promoting the growth of advanced cancers. Smad4, a central TGF? pathway effector, is mutated in ~50% of human PDAC, and Smad4 mutations promote PDAC in mice, consistent with a tumor suppressor function. On the other hand, evidence supporting the TGF? pathway's role in promoting growth of established cancers includes a number of observations from human studies and from our mouse models. Specifically, 1) TGF? pathway activation is associated with advanced human PDAC, and 2) blockade of the TGF? pathway inhibits tumorigenicity of a subset of human and mouse PDAC cells lines. Based on our preliminary data, we hypothesize that TGF-?/Smad4 signaling a) restrains tumor initiation and progression at early stages but b) promotes the malignant growth of a subset of advanced PDAC. Hence inhibitors of TGF? signaling are likely to be effective in the treatment of a subset of metastatic PDAC. This proposal describes a systematic approach to understanding TGF? pathway function throughout each stage of pancreatic ductal tumorigenesis. These studies will employ refine mouse models that enable temporally regulated activation and inactivation of TGF? signaling in vivo and in vivo. We will also use pharmacological approaches to deregulate the pathway. Finally, we will conduct high-throughput assays in PDAC cell lines with known molecular profiles to define markers able to predict responsiveness to TGF? pathway. The Specific Aims are (1) Define the mechanisms by which Smad4 regulates progression of PDAC precursor lesions (PanINs) and the phenotypes of ensuing tumors; (2) Explore TGF? signaling as a target for treatment in advanced PDAC; (3) Determine TGF? pathway components that contribute to tumorigenesis and define molecular markers of TGF? responsiveness in PDAC. Relevance to public health: PDAC is the fourth leading cause of cancer mortality in the United States and is resistant to all existing therapies. Our studies will define the biological roles played by TGF? signaling throughout the course of PDAC progression and thereby provide insight into the potential of this pathway as a drug target. PUBLIC HEALTH RELEVANCE: The TGFbeta pathway is thought to be a good drug target based on the increased activity observed in many advanced cancers including PDAC. While a number of pharmaceutical companies have developed specific anti-TGFbeta drug, their use is complicated by the opposing role of the pathway in limiting cancer initiation. Our proposed experiments will directly investigate the role of TGF-beta signaling at different stages of PDAC progression. The detailed understanding of how alterations in this biochemical pathway affect tumorigenesis will inform help in deciding how to use these drugs in patients in relation to the stage and mutational profile of their disease.